Weather station

Measuring network map DWD from February 12, 2019

An outdoor weather station

Full-time, fully automatic Appental weather station of the DWD in Meßstetten at an altitude of 899.5 meters

A weather station is a collection of various measuring devices that are used to measure meteorological parameters and thus to monitor the weather at a specific location and for climate research .

Weather stations are used for state weather measurements and weather forecasts - such as those of the German Weather Service (DWD) - other weather services and private purposes. A general distinction is made between analog and digital weather stations.

According to the map, the German Weather Service has 210 stations. Of these, around 180 are full-time fully automatic weather stations (without staff). In contrast, about 30 weather stations of the DWD are staffed measuring stations, which will be replaced by fully automatic stations by the end of 2021.

In Austria , ZAMG operates around 250 semi-automatic weather stations. The oldest still existing weather station is the one at the Kremsmünster observatory (Benedictine monastery in Upper Austria). It was established in 1762 and has the longest continuous series of measurements in the world.

Analog weather stations

Clock and weather station on the Aufseßplatz in Nuremberg

Analog weather stations are mostly housed in so-called weather huts (also thermometer huts , climatic huts ). These are small "boxes" made of wood or weather-resistant plastics, which protect the weather instruments from rain and dirt, but at the same time ensure correct readings.

The simple "weather stations" offered in department stores hardly deserve this name. As a rule, they are only designed for indoor use and their thermometers and hygrometers have display errors of up to 3 ° C air temperature and 20% relative humidity .

Weather huts and instruments

The weather huts mentioned above (also called climate huts or English huts) consist of wind-permeable lamellar walls and are painted white on the outside so that the temperature data is not falsified by the solar radiation . A dark surface would absorb more radiation in sunshine , but also with light cloud cover , pass it on to the room air and thus increase the indoor temperature compared to the outdoor temperature. Thus, dark weather huts would always record a temperature that is too high and the systematic error would also vary depending on the weather development (see radiation error ). So that the data from different weather stations can be compared, it has been determined that weather huts must be set up exactly 2 meters above a grassy area and at least 10 meters away from the nearest tree; in addition, the huts should ideally be illuminated by the sun all day and hit by the wind unhindered. As an alternative to the conventional weather huts, smaller radiation protection huts with active ventilation (forced ventilation) are also used for automatic or digital stations (see below). These also consist of lamellar walls, but are also equipped with a power-operated fan so that the smaller dimensions of the housing do not lead to a distortion of the air temperature due to material heating.

The "typical weather hut" is equipped with a psychrometer , maximum and minimum thermometer and a thermohygrograph .

Outside the weather shelter also one's rain gauge in the open air, a anemoscope and an anemometer mounted. Some stations also measure global radiation , the duration of sunshine or special values such as evaporation or soil temperature .

In order to collect data from these analog weather stations, the instruments inside the weather hut must be read . Outside, the water level can be read in the rain gauge or the current wind speed and direction on the anemometer. This happens every hour for full-time stations (for part-time stations only at 7 a.m., 2 p.m. and 9 p.m.), and for rain gauges every morning at 7 a.m.

Advantages of analog stations

no power source required
better assessment of how accurate and reliable the current measured values are.
Observer makes further visual observations (e.g. the course of the weather, visibility ), which are also very valuable and are not necessary with unmanned automatic weather stations.

disadvantage

the weather data is only recorded at certain time intervals (e.g. every hour).
the weather data must always be read "by hand", which entails a considerable cost burden.

Digital weather stations

Weather radar station of the German Weather Service DWD in Dreieich-Offenthal

Digital weather station with some special functions

Digital weather stations essentially have the opposite advantages and disadvantages (see below). They consist of two or more separate parts:

the base station, which receives and evaluates the data

the sensors for the measurement data and the associated data transmission.

The sensors are attached to the desired measuring points , where they collect data and transmit it to the base station. This receives the data (either via cable or radio) and shows it on an LC display . In addition, the data is usually saved for some time and can be called up again if necessary.

More expensive stations also transfer the data to a PC and / or provide an approximate weather forecast for the next few hours.

Different transmission paths are used for remote data transmission (EDI) to a PC. Wired transmission paths using serial data cables, e.g. B. via RS232 / RS485 or dial-up connections via analog, ISDN or radio modems ( GSM , GPRS ). Today's weather stations are also increasingly using data paths based on the Internet protocol. This means that weather data is available via standardized protocols via FTP , HTTP , SNMP in local networks ( LAN ) and wireless networks ( WLAN ), but also worldwide via the Internet . Modern weather stations also send SMS directly . ( Frost warning or current weather data on the mobile phone )

The most commonly used sensors are in detail:

Thermometer (inside and outside), hygrometer (often inside and outside), barometer (mostly inside),
Rain gauge and wind gauge (anemometer) (outside).

Some complex and expensive systems offer additional options such as cloud cover or radiation balance , or are equipped with webcams .

Simple weather forecast

A weather station from bygone times

With the help of the air pressure, some digital weather stations create a weather forecast that provides an approximate forecast of the coming weather. Such a prognosis based solely on the pressure trend is usually very unreliable, since many of the factors responsible for the weather are not taken into account.

More modern stations at least take into account the course of the temperature, some even all data collected outside. Such forecasts are more reliable and locally correct 70 to 90 percent of the time.

The official weather forecasts, on the other hand, reach 80 to 90 percent, but also for larger regions and with more precise information including temperature, wind and amount of rain. An experienced layperson can achieve 70–80% locally even without measurements (only with wind and clouds), while the simplest possible prognosis “today as yesterday” still applies to around 60%.

Sensor connection

If the sensor data are transmitted by radio, this is usually done via the much-used 433 MHz frequency of the 70 centimeter band . Other radio devices that also transmit on this ISM band can interfere with radio reception . Newer models often use the frequency of 868 MHz and work bidirectionally in order to securely transmit measured values in transaction mode .

The range is limited with radio transmission, especially when massive walls have to be penetrated. With radio transmission, all sensors require a power supply; it can be done with solar cells with low consumption .

Wired systems have other limitations. The cables must be long enough to reach the sensors and, in the case of higher demands, also be shielded.

The sensors must be calibrated for legal tasks in accordance with the calibration law .

Advantages of digital stations

The data can be recorded comfortably from the house, whereby a lot of monotonous work and transmission errors due to manual digitization or incorrect reading of the measured values are eliminated.
The measurement values are saved and digitized automatically over a longer period of time.
There are lower maintenance costs, in particular through personnel savings.

disadvantage

Power supply is required
Incorrect data (e.g. from leaves or dirt in the rain gauge, bird droppings on the global radiation sensor, etc.) occur again and again and a manual check of the measuring equipment is therefore often just as necessary as with analog weather stations
The course of the weather is not observed in simple models

literature

Jürgen W. Schmidt: On the history of the weather station on the Schneekoppe. In: Specialized prose research - Crossing borders. Vol. 7, Baden-Baden 2012, pp. 351-370, ISSN 1863-6780 .